Mobile air conditioning system and control mechanisms therefor

ABSTRACT

The performance of mobile air conditioning systems is improved with the use of a pressure sensing valve to control refrigerant flow in the system. The pressure sensing valve is connected between the condenser and the evaporator. The control valve senses the refrigerant pressure adjacent the evaporator, ie. the input, or output, or the combination of both, to control the refrigerant flow through the evaporator in a manner to improve the performance of the system. The reference pressure for the valve can be the atmosphere or a fixed or variable source. Various other operating variables can be sensed to control the variable source in a manner to interact with the sensed pressure to provide added control of system performance.

FIELD OF THE INVENTION

[0001] This invention pertains in general to air conditioning systems,and more particularly to mobile air conditioning systems and controlmechanisms therefor.

BACKGROUND OF THE INVENTION

[0002] The problems involved in the design of effective air conditioningsystems for mobile units are significantly greater Man those involved instationary systems. In general, the basic theory of operation of thestationary and mobile air conditioning units is the same. Each systemrequires a cyclic refrigerant flow through an evaporator to absorb heatfrom the space to be cooled and through a condenser to exhaust theabsorbed heat. However in a stationary system, the compressor is usuallydriven at a constant speed, or in more efficient systems, at two or moreselectable fixed speeds. The more efficient stationary systems may alsohave a selectable multi-speed blower for the evaporator. In any event instationary systems the blower and compressor speeds are knowncontrollable quantities. The uncontrollable variables in the stationarysystems are primarily the ambient temperature of the air or coolantthrough the condenser and the temperature of the air flow through theevaporator.

[0003] In contrast, the mobile air conditioning systems (i.e. systemslocated on mobile vehicles such as in autos, trucks, buses, etc.) facethe same temperature variables involved with the condenser andevaporator and concerning the air flow variables through the evaporator,but in addition include a variable speed compressor whose speed is afunction of the engine speed, and an air flow through the condenser thatis a function or the vehicle speed. All of these additional variablesare controlled by instantaneous vehicle travel requirements, therebygreatly expanding the environmental and physical constraints placed onthe effective operation on the vehicle air conditioning system. Theseadded variables involved in mobile air conditioning systems involve twoextreme situations, i.e., 1) idle when the vehicle is not moving and theengine is running at slow speed (low compressor speed and low condenserair flow ), and 2) road run when both the engine and the vehicle arerunning at high speed ( high compressor speed and high condenser airflow). The problem facing mobile air conditioning system designers areto develop systems that will perform satisfactory at both these extremesand in between.

[0004] An additional problem facing such designers particularly in theautomobile industry is the lack of space and cost control. As automobiledesigns become more compact and greater demands are placed on fuelefficiency and pollution control, there are constant design pressures toreduce the size of elements in the air conditioning systems. Inaddition, as usual there is the on going need to contain or reduce cost.Competing with the constraints of space and cost, there is the continuedneed for improvements in quality of performance. Durability of design isalso a very important factor so as to minimize failures, particularlythose that are catastrophic in nature that result in the destruction ofexpensive elements such a compressor.

[0005] Presently, in mobile air conditioning systems of the type used inautomobiles, the refrigerant flow to the evaporator is controlled eitherby a fixed orifice or a expansion valve. The object of is to attempt toachieve maximum performance by controlling the amount of refrigerant inliquid form as it exits the evaporator (i.e., a point at which most ofthe refrigerant tends to change from liquid to vapor). If totalvaporization of the refrigerant takes place within the evaporator, a hotspot or section is created in the evaporator thereby reducing itseffectiveness. Similarly, the excessive flow of liquid refrigerant fromthe evaporator also reduces the system performance.

[0006] A fixed orifice is an inexpensive means to control refrigerantflow to the evaporator, but suffers the defect that the size of theorifice must be selected as a compromise solution of performance betweenidle and road run. If the size of the orifice is selected to favor idle,then the system will perform favorably in city driving, but will sufferreduced performance in open road driving. In contrast, if the orificesize is selected to favor road run, then city driving suffersperformance.

[0007] Some automobiles use a temperature sensing expansion valve tocontrol the refrigerant flow through the evaporator as a primaryfunction of the refrigerant temperature at the output of the evaporator.The temperature sensing mechanism in an expansion valve is inherentlyslow and therefor not responsive enough to the continually varying airconditioning demands of an automobile. Furthermore, temperature is apoor indication of the condition or state or the refrigerant as itleaves the evaporator in that it can only sense vapor flow and notliquid flow, providing only one half the equation. An additional problemwith the use of the expansion valve is that it tends to fail in theclosed condition, resulting in the shut off of refrigerant and lubricantflow to a level that causes destruction of the compressor.

[0008] It is an object of this invention to provide a new and improvedair conditioning system for mobile air conditioning systems, and controlmechanisms therefor, involving the control of refrigerant flow throughthe air conditioning system evaporator as a function of refrigerantpressure adjacent the evaporator.

BRIEF DESCRIPTION OF THE INVENTION

[0009] In a mobile air conditioning system, control means are providedfor variably controlling the amount of refrigerant flow through the airconditioning system as a function of the refrigerant pressure adjacentto the evaporator. The refrigerant pressure sensing point, or points,for the control means can be adjacent the input or output of theevaporator, or a combination of both. Other variables, such as, ambienttemperature, humidity, engine speed and evaporator temperature areadapted to be sensed and combined with the sensed pressure to providefiner degree of control.

BRIEF DESCRIPTION OF THE FIGURES

[0010]FIG. 1 is a system schematic diagram of a mobile air conditioningsystem of the prior art including a fixed orifice refrigerant controlsystem.

[0011]FIG. 2 is a system schematic diagram of a mobile air conditioningsystem of the prior art including an expansion valve refrigerant controlsystem. FIG. 3 is a system schematic diagram of a mobile airconditioning system including a first embodiment of a refrigerantcontrol system of the invention wherein a pressure sensitive controlvalve is connected to sense evaporator input pressure to controlrefrigerant flow therethrough.

[0012]FIG. 4 is a system schematic diagram of a mobile air conditioningsystem including a second embodiment of a refrigerant control system ofthe invention wherein a pressure sensitive control valve is connected tosense evaporator output pressure to control the flow of refrigeranttherethrough.

[0013]FIG. 5 is a system diagram of a mobile air-conditioning systemincluding a third embodiment of a refrigerant control system of theinvention wherein a pressure sensitive control valve is connected tosense both evaporator input and output pressure to control the flow ofrefrigerant therethrough.

[0014]FIG. 6 is a system diagram of a mobile air conditioning systemincluding a fourth embodiment of a refrigerant control system of theinvention wherein a pressure sensitive control valve is connected tosense evaporator input or output pressure or both to supplement theamount of refrigerant passed by an orifice to an evaporator.

[0015]FIG. 7 is a system diagram of a mobile air conditioning systemincluding a fifth embodiment of the invention of a refrigerant controlsystem of the invention wherein a reference pressure source is providedfor the pressure sensitive control valve, which reference source isvariable and is controllable by a plurality of additional signalscorresponding to added sensed variables.

[0016]FIG. 8 is a mechanical cut away view of a first embodiment of apressure sensitive control valve of the invention for use in the controlof a mobile air conditioning system.

[0017]FIG. 9 is a mechanical cut away view of a second embodiment of apressure sensitive control valve of the invention for use in the controlof a mobile air conditioning system.

[0018]FIG. 10 includes a sketch of a typical pressure-enthalpy chart foran automotive refrigerant with an example of a refrigeration cycleimposed thereon.

[0019]FIG. 11 includes a portion of the mechanical cut away view of thevalve of FIG. 8 modified to include venture type tube configuration atthe point the pressure is sensed.

[0020]FIG. 12 includes a portion of the mechanical cut away view of thevalve of FIG. 8 modified to include stepped orifice type configurationat the point the pressure is sensed.

DETAILED DESCRIPTION

[0021] The prior art mobile air conditioning system of FIG. 1 includes acompressor 10 that is coupled to be driven by an engine that propels themobile unit (not illustrated). In the case of an automobile thecompressor is driven by the engine via a belt coupled to the compressor10 clutch-pulley 12. The speed at which the compressor 10 is rotated isa function of the speed of rotation of the engine. Hence the higher thespeed of the rotation of the engine rotation, the higher speed ofrotation of the compressor 10 and the correspondingly higher capacity ofthe compressor 10 to pump refrigerant, and thereby accompanied by ahigher output refrigerant pressure capability.

[0022] The direction of the flow of the refrigerant through the systemis illustrated by the arrows 14. A compressed high pressure gaseousrefrigerant flows from the compressor 10 through a condenser 16. Thepurpose of the condenser 16 is to reject heat from the air conditioningsystem, while at the same time condenses the high pressure gaseousrefrigerant into high pressure liquid refrigerant at the condenser 16output. High pressure within the condenser is needed to causeliquidification of the refrigerant. In air conditioning systems formobile units, air flow through the condenser 16 absorbs heat from therefrigerant flow. The flow of air through the condenser 16 is variableie. the faster the mobile unit is traveling, or the faster the enginefan is rotating, or the combination of both, the greater the air flowand therefor the greater the capacity for heat rejection from thecondenser 16, and visa versa. At times an added blower is provided withthe condenser 16 to enhance air flow at slow mobile unit travel speed.

[0023] The high pressure liquid refrigerant flows from the condenser 16through an orifice tube 18 to an evaporator 20. The orifice tube 18includes a fixed size of opening to allow the high pressure build up bythe compressor, and restricts the amount of refrigerant flow though outthe air conditioning system and in particular the amount of refrigerantflow through the evaporator 20. The refrigerant flow as it passesthrough the orifice, flashes across the orifice to form a foam typeliquid refrigerant output that flows into the evaporator. Ideally a lowtemperature, low pressure all liquid refrigerant flow should enter theevaporator 20 and the refrigerant at the evaporator 20 output should beall vapor at its saturation temperature (boiling point). It is thisboiling of the refrigerant within the evaporator 20 that changes theliquid refrigerant to vapor that causes the beat absorption and providesthe cooling effect of the evaporator 20. The closer the evaporator 20approaches the ideal condition, the greater its cooling effectiveness.Should the refrigerant boil off entirely somewhere within the evaporator20, the vaporized refrigerant flow within the evaporator 20 will causehot spots within the evaporator 20 and result in an associated loss ofeffectiveness. Correspondingly a flow of liquid refrigerant from theevaporator 20 also causes a loss in system performance.

[0024] The refrigerant output from the evaporator 20 flows through anaccumulator 22 to the compressor 10. If liquid refrigerant flows fromthe evaporator 20, the accumulator 22 will accumulate the liquid if noliquid refrigerant is received then the accumulator 22 bleeds out storedliquid into the system. In effect the accumulator 22 controls the amountof active refrigerant charge in the system. Further, it is thecombination of the orifice 18 and the accumulator 22 that controls therefrigerant flow through the system. An orifice system is designed tooperate so that a little liquid refrigerant flows from the evaporator 20into the accumulator 22. If too much liquid refrigerant flows from theevaporator 20, the accumulator 22 acts as a liquid/vapor separator andstarts to fill up with liquid refrigerant and thereby takes refrigerantcharge from the active system. If no liquid refrigerant flows from theevaporator 20, the accumulator 22 will bleed out liquid refrigerant intothe active system, thereby keeping the system properly charged. Theaccumulator 22 can also include a dehydrator to remove any water thatmay have been trapped in the system.

[0025] As previously mentioned, the size of the fixed orifice 18 isselected as a compromise solution between system operation for idle orroad run. If set for idle, the system performance will favor citydriving, but will suffer reduced performance in open road driving. Incontrast, if set to favor road run, then city driving will suffer inperformance. If set in between, system performance capability will notbe achieved at idle or road run.

[0026] For purposes of simplifying the explanation of the invention,FIGS. 1-7 will have the same reference numerals for the same elements,In the prior art system of FIG. 2 the orifice of FIG. 1 has beenreplaced by a temperature sensing expansion valve 24. The expansionvalve 24 includes a charged bulb that senses evaporator 20 outputtemperature by increasing the pressure within the bulb as a directfunction of temperature ie. as temperature goes up the pressure withinthe bulb goes up and via versa. The pressure within the bulb urgesagainst a diaphragm that has evaporator 20 output refrigerant pressureas a reference on the other side of the diaphragm. The diaphragmoperates the valve mechanism and controls the refrigerant flowtherethrough. When an expansion valve is used in a mobile airconditioning system the expansion valve is set so that no liquidrefrigerant flows from the evaporator 20. This is done by setting theexpansion valve to control refrigerant flow so that the temperature ofthe refrigerant as it exits the evaporator 20 is always beyond theboiling point of the refrigerant. Therefor, since no liquid refrigerantflows from the evaporator 20, there is no need of an accumulator, andinstead the system of FIG. 2 includes a receiver 26 at the output of thecondenser 16. The receiver 26 functions to separate out vapor bubbles toprovide a solid liquid column to the expansion valve 24. The receiver 26may also include a dehydrator.

[0027] Although the temperature sensitive valve 24 may in certaincircumstances provide for better operation through its variable controlof refrigerant flow though the evaporator 20, the fact that the valve 24is based on temperature sensing creates limitations on itseffectiveness. For example, the temperature sensing unit is inherentlyslow responding, thereby limiting the capability of the valve topromptly respond to system needs. In addition, because the expansionvalve is temperature sensing, it can not sense whether or not any liquidrefrigerant is present. To prevent excessive liquid refrigerant flowfrom the evaporator 20, the flow through the evaporator needs to becontrolled in a manner that the refrigerant as it exits the evaporator20 must be above its boiling (all vapor). To accomplish this theexpansion valve temperature sensor is set to control the refrigerantflow through the evaporator 20 so that the temperature of therefrigerant as it exits the evaporator is several degrees above boiling(all vapor). To maintain this exit temperature, the refrigerant mustreach its boiling point within the evaporator. As a result, with vaporwithin the evaporator 20, a corresponding portion of the evaporator willlose its cooling capability ( hot spots ). A modification to theexpansion valve was attempted by the use of an electronic liquidrefrigerant detector which would heat valve temperature sensor, but wasfound to be slow in responding. Hence the expansion valve is only apartial, and more expensive, solution to the problems of the orificetype mobile air conditioning system. Therefor since the orifice providesa low cost compromise solution, the orifice tends to more extensivelyused despite its limitations.

[0028] In FIG. 3 the first embodiment of the mobile air conditioningsystem of the invention includes a pressure sensitive control valve 28instead of the fixed orifice 18. The valve 28 has a variable openingthat controls the flow of refrigerant flow therethrough as a function ofthe refrigerant pressure at the input 30 of the evaporator 20.

[0029] In FIG. 4 the second embodiment of the mobile air conditioningsystem of the invention includes a pressure sensitive control valve 32.The valve 32 has a variable opening that controls the flow ofrefrigerant flow therethrough as a function of the refrigerant pressureat the output 34 of the evaporator 20.

[0030] In FIG. 5 the third embodiment of the mobile air conditioningsystem of the invention includes a pressure sensitive control valve 35that is connected to sense both the evaporator input and outputpressure.

[0031] In FIG. 6 the fourth embodiment of the mobile air conditioningsystem of the invention includes a pressure sensitive control valve 36that is connected in parallel with the orifice 18 to supplement the flowof refrigerant through the orifice 18. As in FIG. 3, the valve 36 isconnected to be controlled by the refrigerant at the evaporator input34, but the valve could alternately be connected to monitor theevaporator 20 output pressure 34 (as illustrated by the dashedconnection 37) in accordance with FIG. 4. Still further, the embodimentof Figure could be further modified to sense both the evaporator inputand output pressure in a manner as illustrated in FIG. 5. In thisembodiment the size of the fixed opening in the orifice 18 would beselected on the small size with valve 36 providing the added refrigerantflow to improve system performance.

[0032] In the fifth embodiment of the invention of FIG. 7, the pressuresensitive control valve 39 is connected to sense the evaporator inputpressure. A reference source 38 is connected to a pressure input port 40of the valve 39 to provide a reference pressure to which the evaporatoroutput pressure can be compared. The reference source 38 can be a fixedtype, or a variable type as illustrated. If variable, the outputpressure of the source 38 can be controlled by a number of inputs. Forexample a ambient temperature sensor 42 (already provided with some airconditioning systems), an engine speed sensor 43 (tachometer), ahumidity sensor 44, an evaporator 20 output temperature sensor 45 and avehicle speed sensor 47 (speedometer) can be connected via analog todigital converters and sample and hold circuits 51 to the vehiclecomputer 46. The computer 46 can periodically scan each sample and holdcircuit 51 in sequence and transfer the various read outs into memory57. The computer 46 can be conventionally programmed to provide aweighing factor to each of the scanned variables, relative to thecontrol valve 39 sensed refrigerant pressure, that can be tailored tofunction with the characteristics of the mobile air conditioning systemto which the control system of the invention is being applied. Thecomputer 46 will periodically analyze all the inputs and provide andoutput signal to a sample and hold circuit and digital to analogconverter 53 that will store the signal between analysis. The output ofthe sample and hold circuit will be applied to a digital to analogconverter circuit to provide a composite electrical control signal tocontrol the output of the reference source 38. The composite controlsignal functions to supplement the evaporator input pressure as thesystem control function. For example, if the ambient humidity increases,or the ambient temperature increases, or the evaporator 20 outputtemperature increases, the contribution of these variable input signals,alone, or in combination, will be in a direction to create an input tothe composite control signal in a direction to increase refrigerant flow(and vica versa). In contrast, if the engine speed increases, or thevehicle speed increases, the contribution of these variable inputsignals, alone, or in combination, will be in a direction to decreaserefrigerant flow. The composite output signal from the computer 46 willfunction via the variable source 38 in a manner to supplement therefrigerant pressure sensing control to provide to a means by which thecontrol system of the invention can better respond to the multitude ofvariables that impact the mobile air conditioning system performance.Although FIG. 7 illustrates a control system that includes a pressuresensitive valve that senses evaporator input pressure, alternately thevalve can sense the evporator output pressure and the evaporator inputpressure can then be sensed electronically.

[0033] The embodiment of the pressure controlled valve 48 of theinvention illustrated in FIG. 8 includes an inlet 50 adapted to beconnected to receive refrigerant flow from the condenser 16 and anoutlet 52 adapted to be connected to transmit refrigerant flow to theevaporator 20. The amount of refrigerant flow is controlled by theposition of the valve stem 54 edge 56 relative to the valve seat 58. Thevalve stem 54 is connected to a pin 60, a part of which is located inthe pin bearing 62, so that the pin 60 can move along the bearing 62.The pin end 64 is pressed fit into a follower 66 which in turn isconnected to a diaphragm 68. A fine tune adjustment spring 70 is locatedbetween the opposite end 72 of the pin stem 54 and a fine tune adjustingscrew 74, so as to provide a pressure on the end 72 to urge the follower66 against the diaphragm 68. The diaphragm 68 is connected and ispressure sealed at its ends to the diaphragm chamber 78 which in turn ismounted by a sealed connection 79 to the valve 48 casing 81. Anatmospheric or reference pressure compensation spring 80 is connectedbetween vent 82 and a spring follower 84 which urges against theopposite side of the diaphragm 68. The vent 82 may be mounted in placeto the vent chamber 83 by a pressure fit, or if an added adjustment isdesired, may be mounted with a threaded connection wherein the vent 82may be rotated to provide an adjustment for setting the pressure beingapplied by the compensation spring 80.

[0034] The evaporator input refrigerant pressure is sensed by the valve48 by a refrigerant pressure sensing path 86 coupled between the valvestem cavity 88 and the diaphragm cavity 90. The casing 81 and thediaphragm cavity 90, when the valve 48 is connected into the airconditioning system, form a sealed chamber for the sensed refrigerant atthe evaporator input. As the pressure increases, the added pressure onthe diaphragm causes the diaphragm to flex in a direction to move thestem 56 to reduce the spacing between the stem edge 56 and the valveseat 58 and thereby reduce the size of the opening 92 available forrefrigerant flow. When the evaporator input pressure decreases thediaphragm 68 causes the size of the opening 92 to increase. Hence, ascan be seen the valve 48 functions so as to control the size of theopening 92 as an inverse function of the evaporator input pressure ie.as pressure goes up, the size of the opening 92 decreases, and vicsaversa.

[0035] In the description of the pressure controlled valve 94 of theinvention of FIG. 9, for the purpose of simplifying the description, thesame elements in FIGS. 8 and 9 will have the same reference numerals. InFIG. 9, the flow path 86 of FIG. 8 is eliminated and an evaporatoroutput pressure sensing path 96 is substituted in its place. Thepressure sensing path 96 is adapted to be connected to the evaporatoroutput 34 of FIGS. 4,5 and 6 by suitable coupling means. In addition,the valve 94 of FIG. 9 will also include an O ring 97 between the pin 60and bearing 62 so to provide isolation between the evaporator inputrefrigerant in the valve stem cavity 88 and the diaphragm cavity 90. Thevalve 94 will control the size of the opening 92 as an inverse functionof the pressure in the diaphragm cavity 90 evaporator output pressure inthe same manner as described with regard to FIG. 8.

[0036] In both the embodiments of the pressure controlled valves ofFIGS. 8 and 9, the amount of travel of the pin 54 is selected andadjusted by the spring 70 (and spring 80 if made adjustable) so that asthe refrigerant input pressure to the diaphragm chamber 90 can move thepin 54 to cover the desired range of adjustment of the opening 92. Thearrangement is such that the opening 92 never closes beyond the point ofminimum refrigerant flow needed to maintain the compressor 10 operableso that a breakdown in the valves 48 or 94 does not shut off therefrigerant flow to a level to cause compressor failure.

[0037] The valves 48 and 94 of FIGS. 8 and 9 can be modified so as tothe vent can be coupled as the port 40 to pressure source 38 of FIGS. 5,6 and 7 instead. The pressure source 38 can be designed to be less thanatmospheric pressure (vacuum) or greater than atmospheric pressure(positive pressure) depending on design preferences. An increase inpressure applied to the vent 82 will reduce the effect of the pressurein the diaphragm cavity 90 and will reduce the valve opening 92, andvicsa versa.

[0038] The designs of the valves 48 and 94 of FIGS. 8 and 9 can becombined to sense both the evaporator 20 input and output pressure asillustrated in FIG. 6, by including the input pressure sensing path 86or the output pressure sensing path 96, and by using the vent 82 as theport 40 to provide a path for sensing the other evaporator input oroutput pressure.

[0039] The evaporators 20 come in a variety of designs, ie. “S” flow,“U” flow, multipath flow, etc., depending on various design criterionsand the pressure drop across the evaporator. The pressure drop may beless than 2 lbs. and greater than 10 lbs. With the lower pressure droptype evaporators it is preferred to use the input pressure sensing valveof FIG. 8 in the embodiment of FIG. 3. If the evaporator 20 is of thetype that exhibits higher pressure drop the valve 94 of FIG. 9 may bepreferred to be used in the embodiments of FIGS. 4, 5, 6 and 7(depending upon design criterions).

[0040] The control valves 48 and 94 of the invention of FIGS. 8 and 9primarily sense pressure and changes therein, and when incorporated intoa mobile air conditioning system as described herein, have a very rapidresponse time as compared to the much slower temperature sensingmechanism of the expansion valves of the prior art. Therefor thepressure sensitive valves of the invention provide a more responsivecontrol that can more readily adjust to the continuous changing drivingconditions and the input variables as described in detail above.Further, in contrast to the expansion valve of the prior art, thecontrol valves of the invention disclose a design for a valve mechanismthat has a sufficient degree of adjustment to provide the desireddegrees of refrigerant flow control, while at the same time provides forlimited travel so that the valve mechanism will not fail in the closedmode. This assures ample refrigerant flow to the compressor to preventcompressor break down should the valve fail. The cost of the valve ofthe invention based on the pressure sensing design can be significantlyless than the more complex thermal sensing mechanism of the expansionvalves of the prior art. Still further, as discussed above, a valveembodying the invention, in its capability in sensing either evaporatorinput pressure, or output pressure, or both, and with appropriatemodifications as also discussed, has application for use with a varietyof high, low, or intermediate pressure drop evaporators. Valvesembodying the invention in addition also have the capability to becombined with a variable pressure (or vacuum) source. The variablesource can provide an added signal input by which other variables can becombined with the sensed pressure to provide added control to enhancethe performance of mobile air conditioning systems.

[0041] As previously mentioned above, in an orifice accumulator typesystem, it is the accumulator that controls or regulates the amount ofactive refrigerant charge in the system, and it is the combination ofthe orifice and the accumulator that control the refrigerant flowthrough the system. When excess refrigerant flows to the evaporator, theliquid overspill collects in the accumulator. This excess liquidrefrigerant is held in the accumulator, thereby reducing the effectiverefrigerant charge in the system. On the other hand, when too littlerefrigerant flows into the evaporator, the accumulator adds morerefrigerant into the system through the bleed hole. This addition andextraction of refrigerant to the system increases flow to the evaporatordue to the increased amount of refrigerant in the condensing side of theair conditioning system. This addition and extraction of refrigerant tothe effective refrigerant system along with the orifice size (valveopening) provides the evaporator refrigerant flow control.

[0042] In effect the control valves 28, 32, 35, 36, and 39, of FIGS. 3,4, 5, 6, and 7, respectively, function as variable orifices in anorifice accumulator type air conditioning system that provide for acontrolled flooded evaporator operation as the compressor and condensercapacities change. This is in contrast to the expansion valve receivertype system of FIG. 2. The valves receive the liquid refrigerant fromthe condenser and like the orifice, flash the liquid into a combinationof majority liquid and some vapor during which time there is atemperature and pressure drop in the refrigerant as it flows into theevaporator. As mentioned above, since the valve will not entirely close,the opening in the valve will vary between upper and lower limits. Theselimits will change for different vehicular air conditioning designs tosatisfy the required refrigerant flow rates in the various system designspecifications. As an example, an air conditioning system that delivers24,000 BTU/Hr. at maximum cooling loads may have a valve with an openingthat varies to provide an effective variable orifice with operationlimits corresponding to 0.075 inches diameter to 0.045 inches diameter.

[0043] The valves sense the pressure of the refrigerant adjacent to theevaporator 16, at the input (FIGS. 3 and 7), at the output (FIG. 4), atthe input and the output (FIGS. 5 and 6) to control the size of thevalve opening (instantaneous orifice size). The pressure drop across anevaporator is a function of the amount of refrigerant flow therethrough. As mentioned above, the pressure drop across various models ofevaporators is known or can be measured. If the input pressure is beingmeasured, since the pressure drop for any evaporator design is known,the input pressure when adjusted for an average known evaporatorpressure drop is in effect a good approximation of evaporator outputpressure. As mentioned above, the control of the valve provides aninfinite number of orifice sizes between the limits of operation isinversely proportional to the evaporator pressure. This means that asthe sensed pressure increases, the size of the opening in the valvedecreases. Conversely, as the sensed pressure decreases, the opening inthe valve increases.

[0044] The arrangement is such that as the refrigerant pumping capacityof the compressor changes due to changes in engine speed, or as the heatrejection capacity of the condenser changes due to changes in air flowthere through resulting from changes in vehicle speed and engine fanspeed, or both, the valve, acting as an variable orifice, responds tothe sensed refrigerant pressure to vary the valve opening in a directionto enhance the cooling capacity of the system. For example, if thecapacity of the condenser and compressor increase, such as by vehicleacceleration to the road run condition, the valve adjusts the size ofthe opening in a direction to take advantage of the increased capacitiesto increase the cooling capacity of the system. On the other hand, ifsuch vehicle slows to an idle condition, then the valve adjusts theopening so as conform the system to lower compressor and condensercapacities while preventing excess liquid refrigerant flow to theaccumulator. Hence as can be seen, the variable orifice effect of thevalve tailors the system operation for enhanced operation for highcompressor and condenser capacities during high speed road run, and forlower capacities at idle, and for various capacities in between.

[0045] As mentioned above, for ideal evaporator operation, thesubstantially all liquid refrigerant from the valves should enter theevaporator and the refrigerant at the evaporator output should be allvapor at its saturation temperature (boiling point). However, in anorifice accumulator type of system the output refrigerant should besubstantially total vapor, ie. vapor with a low level of liquid flow asneeded by the accumulator to keep the system charged. The operation ofthe valves are set to function, over the above mentioned changes incompressor and condenser capacities, so as to control the valve openingin a direction for pressures at the output of the evaporator thatcorresponds to a situation wherein the entire evaporator is filled withat least some liquid refrigerant (corresponding to saturated liquidrefrigerant at saturated temperature, ie the boiling point of liquidrefrigerant) so as to have a refrigerant boiling action through out theevaporator to achieve heat absorption over the entire evaporator, whilehaving saturated refrigerant vapor at substantially total vaporization(vapor refrigerant at boiling point) adjacent the output of theevaporator so as to provide the controlled level of a small amount ofliquid refrigerant to the accumulator as may needed to keep the activerefrigerant flow properly charged.

[0046] The valve interacts with the accumulator control the flow ofrefrigerant in the system with changes in compressor and condensercapacities in a direction toward evaporator output pressures that followthe refrigerant pressures in the pressure-enthalpy diagram of FIG. 10along the right hand portion 100 of the bell type shaped curve 102marking the division between saturated vapor and total vaporization. Therefrigerant within the bell shaped curve 102 changes from entirelyliquid at the left hand portion 104 to entirely vapor at the right handportion 100, with decreasing level of liquid and increasing levels ofvapor from left hand portion 104 to the right hand portion 100. Therefrigerant cycle 106 on the pressure-enthalpy diagram includes an upperhorizontal dashed line 108 representing the action of the condenseraction of liquefy the refrigerant and extends beyond the bell shapedcurve on both sides. The above mentioned refrigerant flashing action ofthe orifice or valves can be represented by a vertical dashed line 110extending downward from the end of the horizontal line 108 to pointswithin the bell shaped curve 102 wherein the majority of the refrigerantis liquid. The evaporator action can be represented by the horizontaldashed line 112 extending from the vertical line across the bell shapedcurve 102 within the bell shaped curve, or to, or beyond, the right handportion 100 of the bell shaped curve. The refrigeration cycle 102 iscompleted by the generally vertical dashed line 114 extending upwardfrom the end of the horizontal evaporator line 112 to the horizontalcondenser line 108 representing the action of the compressor.

[0047] The relationship of the various dashed lines depends upon theoperation of the air conditioning system. If the system is operatingalong this horizontal line 112 with an evaporator output pressurecorresponding to saturated vapor within the bell shaped curve 102, theevaporator will output liquid, the amount of which will depend on therefrigerant pressure. In the case of the larger fixed orifice of theprior art (tailored for road run), during idle the output pressure wouldfall within the bell shaped curve 102 to a degree to cause theevaporator to output liquid which will fill the accumulator to reducethe active charge in the system and thereby reduce the cooling capacityof the system. In the case of the small fixed orifice of the prior art(tailored for idle), during road run the output pressure would risewithin the evaporator to prematurely reach the right hand portion 100 ofthe bell shaped curve 102 within the evaporator thereby causing totalvaporization within the evaporator and the creation of the undesirablehot spots. With the control system of the invention, the flow ofrefrigerant can be controlled in the system as the various compressorand condenser capacities change in a direction so that the evaporatoroutput pressures (represented by junction 118) closely follow the righthand portion 100 of the curve 102 in a manner to either stay, justinside the right hand portion 100 of the bell shaped curve 102, or moveback and forth about and close to the right hand portion 100, ascapacities change so as to reduce the likelihood of the creation of hotspots with in the evaporator while also providing the low level ofliquid refrigerant flow to the accumulator to keep the system charged.

[0048] During periods of high refrigerant flow through the evaporator,the pressure drop across the evaporator may vary by an amount from theaverage, or design criterion, of the evaporator so that some addedcompensation may be desired for the valve of FIG. 8 for added controlduring the high refrigerant flow rates. In such case, instead ofmeasuring the pressure at the valve stem cavity 88, the wall portions ofthe valve adjacent the sensing path 86 can be modified so to the formthe venturi tube 120 of FIG. 11 (a contraction with a subsequentexpansion), or a stepped orifice 124 of FIG. 12 (an expansion) and apressure sensing path 126 connected at the point of expansion 128 of thestepped orifice 124. With the embodiments of pressure sensing of FIGS.11 and 12, the pressure measurement will have a compensating factorbased on the refrigeration flow rate.

[0049] In addition, although the valve or variable orifice 32 of FIG. 4is illustrated as being physically located adjacent the input of theevaporator 20, it should be understood that the valve 32 could just aswell be located adjacent the output of the evaporator 20 in a manner inwhich the temperature sensing valve 24 of FIG. 2 is located, so as toreduce the length of the connection between the evaporator output 34 andthe valve 24 an allow the valve 32 to be more responsive.

What is claimed:
 1. A pressure sensitive valve adapted to control theamount of refrigerant flow in vehicular air conditioning systems thatinclude a compressor, a condenser, an evaporator and an accumulatorinterconnected for serial refrigerant flow therein, and wherein thevehicle engine drives the compressor so that the refrigerant pumpingcapacity of the compressor increases and decreases with increases anddecreases in vehicle engine speed, and the heat rejection capacity ofthe condenser increases and decreases in air flow there through due toincreases and decreases in the vehicle speed and engine fan speed, saidvalve comprising: a casing for the valve including an input port adaptedto be connected to receive refrigerant from the condenser, and an outputport adapted to be connected to deliver the refrigerant to theevaporator; a variable valve located within the casing between the inletport and the output port for controlling the size of the opening betweenthe ports; a pressure sensing mechanism adapted to be connected forsensing refrigerant pressure adjacent the evaporator to provide adisplacement motion that is a function of the magnitude of the sensedpressure, and a coupling mechanism connected between the pressuresensing mechanism and the variable valve to control the size of theopening as a function of the magnitude of the sensed pressure, so thatthe variable valve is adapted to function as a variable orifice andinteract with the accumulator to control the amount of refrigerant flowthrough the system so as to vary the cooling capacity of the systemrelative to changes in at least one of the compressor and condensercapacities.
 2. A refrigerant control system of claim 1 wherein theaccumulator accumulates liquid refrigerant from the evaporator andbleeds off accumulated liquid refrigerant keep the system charged.
 3. Apressure sensitive valve of claim 1 wherein the valve opening increasesto increase refrigerant flow with increases in compressor capacity anddecreases to decrease refrigerant flow with decreases in compressorcapacity.
 4. A pressure sensitive valve of claim 3 wherein the valveopening increases to increase refrigerant flow with increases incondenser capacity and decreases to decrease refrigerant flow withdecreases in condenser capacity.
 5. A pressure sensitive valve of claim1 wherein the range of operation of the variable valve is limited sothat the opening does not close.
 6. A pressure sensitive valve of claim1 wherein the sensed pressure is adapted to be received from thepressure of the refrigerant adjacent the valve output port.
 7. Arefrigerant control system of claim 1 wherein the pressure sensitivemechanism is adapted to sense evaporator output refrigerant pressure. 8.A pressure sensitive valve of claim 7 wherein a second sensedrefrigerant pressure is also adapted to be received and combined withrefrigerant pressure from the output port to provide a combined senseddifferential pressure.
 9. A pressure sensitive valve of claim 1 whereinthe valve is adapted to control the size of the valve opening in adirection toward evaporator refrigerant pressure at the output of theevaporator corresponding to saturated refrigerant vapor at substantiallytotal vaporization adjacent the output of the evaporator andsubstantially total saturated liquid refrigerant at saturationtemperature within the evaporator.
 10. A pressure sensitive valve ofclaim 1 including a reference port adapted to provide a pressurereference source wherein the pressure sensing mechanism senses thepressure difference between the sensed pressure and the referencepressure to provide the displacement motion.
 11. A pressure sensitivevalve of claim 10 wherein the reference port is adapted to be exposed tothe atmosphere as the reference pressure.
 12. In a vehicular airconditioning system including a compressor, a condenser, an evaporatorand an accumulator connected in series for cyclic refrigerant flowtherein wherein the vehicle engine drives the compressor so that thecompressor capacity is a function of engine speed, and the capacity ofthe condenser is a function the vehicle speed and engine fan speed, acontrol system for controlling refrigerant flow in the systemcomprising: a pressure sensitive control valve having an input port, anoutput port, a variable valve mechanism there between having a variableopening for connecting the input port to the output port and a pressuresensing mechanism coupled to the variable valve mechanism for providinga displacement movement thereto for controlling the size of the openingof the valve mechanism; means for coupling the input and output ports ofthe pressure sensitive valve in the air conditioning system at a pointbetween the condenser and the evaporator, and means for coupling thepressure sensing mechanism to sense the refrigerant pressure adjacent tothe evaporator so that the valve function as a variable orifice tocontrol the amount of refrigerant flow through the system so as to varythe cooling capacity of the system relative to changes in at least oneof the compressor and condenser capacities.
 13. A refrigerant controlsystem of claim 12 wherein the pressure sensitive mechanism sensesevaporator input refrigerant pressure.
 14. A refrigerant control systemof claim 12 wherein the pressure sensitive mechanism senses evaporatoroutput refrigerant pressure.
 15. A refrigerant control system of claim12 wherein the pressure sensitive mechanism senses both the input andoutput evaporator refrigerant pressure.
 16. A refrigerant control systemof claim 12 wherein the pressure sensitive mechanism includes areference port for receiving a reference pressure for comparing thesensed pressure with the reference pressure and for providing thedisplacement motion as a function of the pressure difference therebetween.
 17. A refrigerant control system of claim 16 wherein thereference pressure is the atmospheric pressure.
 18. A refrigerantcontrol system of claim 16 wherein the reference pressure source isadjustable and including means for sensing ambient temperature foradjusting the reference pressure source in a direction so that thedifferential pressure is in a direction to increase the size of thevalve opening.
 19. A refrigerant control system of claim 16 wherein thereference pressure source is adjustable and including means for sensingambient humidity for adjusting the reference pressure source in adirection so that the differential pressure is in a direction toincrease the size of the valve opening.
 20. A refrigerant control systemof claim 16 wherein the reference pressure source is adjustable andincluding means for sensing vehicle speed for adjusting the referencepressure source in a direction so that the differential pressure is in adirection to decrease the size of the valve opening.
 21. A refrigerantcontrol system of claim 16 wherein the reference pressure source isadjustable and including means for sensing engine speed for adjustingthe reference pressure source in a direction so that the differentialpressure is in a direction to decrease the size of the valve opening.22. A refrigerant control system of claim 16 wherein the referencepressure source is adjustable and including means for sensing evaporatoroutput temperature for adjusting the reference pressure source in adirection so that the differential pressure is in a direction toincrease the size of the valve opening.
 23. A refrigerant control systemof claim 12 wherein an orifice is connected in parallel to the pressuresensitive valve.
 24. A refrigerant control system of claim 12 whereinthe accumulator accumulates liquid refrigerant from the evaporator andbleeds off accumulated liquid refrigerant to maintain the refrigerantcharge of the system.
 25. A refrigerant control system claim 12 whereinthe valve controls the size of the valve opening in a direction towardevaporator refrigerant pressure at the output of the evaporatorcorresponding to saturated refrigerant vapor at substantially totalvaporization adjacent the output of the evaporator and substantiallytotal saturated liquid refrigerant at saturation temperature within theevaporator.
 26. In a mobile air conditioning system including acompressor, a condenser, an evaporator and an accumulator connected inseries for cyclic refrigerant flow therein, wherein the vehicle enginedrives the compressor so that the compressor capacity is a function ofengine speed, and the capacity of the condenser is a function thevehicle speed and engine fan speed, a control system for controlling theflow of refrigerant flow in the system comprising: a control valveconnected in the system between the condenser and the evaporator tocontrol the refrigerant flow through the system, said control valvebeing responsive to input signals to vary the flow of refrigerant flowthere through; a sensor for detecting refrigerant pressure adjacent tothe evaporator and at least one of a plurality of variables includingambient temperature, ambient humidity, engine speed, vehicle speed andevaporator output temperature, and means for combining the output of thepressure sensor with at least the output of one of the plurality ofvariables as input signals to the control valve to control therefrigerant flow in the system with changes in at least one of thecompress and condenser capacities.
 27. A pressure sensitive valveadapted to control the amount of refrigerant flow in vehicle airconditioning systems that include a compressor, a condenser, anevaporator and an accumulator interconnected for serial refrigerant flowtherein, and wherein the vehicle engine drives the compressor so thatthe refrigerant pumping capacity of the compressor increases anddecreases with increases and decreases in vehicle engine speed, and theheat rejection capacity of the condenser increases and decreases withair flow there through with increases and decreases in vehicle speed andengine fan speed, said valve comprising: a casing for the valveincluding an input port adapted to be connected to receive refrigerantfrom the condenser, and a output port adapted to be connected to deliverthe refrigerant to the evaporator; a variable valve located within thecasing between the inlet port and the output port for controlling thesize of the opening between the ports; a pressure sensing mechanismadapted to be connected for sensing evaporator refrigerant pressureadjacent the evaporator to provide a displacement motion that is afunction of the magnitude of the sensed pressure, and a couplingmechanism adapted to be connected between the pressure sensing mechanismand the variable valve to control the size of the opening as a functionof the magnitude of the sensed pressure in a direction towardsevaporator refrigerant pressures adjacent the output of the evaporatorcorresponding to substantially total refrigerant vaporization so as tocontrol the heat absorbing capacity of the evaporator relative tochanges in at least one of the compressor and condenser capacities. 28.A refrigerant control system of claim 27 wherein the accumulatoraccumulates liquid from the substantially totally vaporized refrigerantoutputted by the evaporator and bleeds off the accumulated liquidrefrigerant to keep the system charged.
 29. A pressure sensitive valveof claim 28 wherein the variable valve is responsive to the displacementaction of the pressure sensitive mechanism to control the size of thevalve opening in a direction toward evaporator refrigerant pressurecorresponding to saturated refrigerant vapor at substantially totalvaporization adjacent the output of the evaporator and substantiallytotal saturated liquid refrigerant at saturation temperature within theevaporator.
 30. A pressure sensitive valve of claim 27 wherein the sizeof the valve opening increases to increase refrigerant flow withincreases in compressor capacity and decreases to decrease refrigerantflow with decreases in compressor capacity.
 31. A pressure sensitivevalve of claim 30 wherein the size of the valve opening increases toincrease refrigerant flow with increases in condenser capacity anddecreases to decrease refrigerant flow with decreases in condensercapacity.
 32. A pressure sensitive valve of claim 27 wherein thepressure sensing mechanism measures pressure adjacent the input of theevaporator.
 33. In a vehicular air conditioning system including acompressor, a condenser, an evaporator and an accumulator connected inseries for cyclic refrigerant flow therein and wherein the vehicleengine drives the compressor so that the refrigerant pumping capacity ofthe compressor increases and decreases with increases and decreases invehicle engine speed, and the heat rejection capacity of the condenserincreases and decreases with air flow there through with increases anddecreases in vehicle speed and engine fan speed, a control system forcontrolling the flow of refrigerant flow in the system comprising: apressure sensitive control valve having an input port an output port avariable valve mechanism there between having a variable opening forconnecting the input port to the output port and a pressure sensingmechanism coupled to the variable valve mechanism for providing adisplacement movement thereto for controlling the size of the opening ofthe valve mechanism; means for coupling the input and output ports ofthe pressure sensitive valve in the air conditioning system at a pointbetween the condenser and the evaporator, and means for coupling thepressure sensing mechanism to sense the refrigerant pressure adjacent tothe evaporator to control the refrigerant flow through the valvemechanism as a function of the magnitude of the sensed pressure in adirection toward evaporator pressures adjacent the output of theevaporator corresponding to substantially total refrigerant vaporizationso as to control the heat absorbing capacity of the evaporator relativeto changes in at least one of the compressor and condenser capacities.34. A control system of claim 33 wherein the accumulator accumulatesliquid from the substantially totally vaporized refrigerant outputted bythe evaporator and bleeds off the accumulated liquid refrigerant to keepthe system charged.
 35. A control system of claim 33 wherein thevariable valve is responsive to the displacement action of the pressuresensitive mechanism to control the size of the valve opening in adirection towards evaporator refrigerant pressures corresponding tosaturated refrigerant vapor at substantially total vaporization adjacentthe output of the evaporator and substantially total saturated liquidrefrigerant at saturation temperature within the evaporator.
 36. Acontrol system of claim 33 wherein the size of the valve openingincreases to increase refrigerant flow with increases in compressorcapacity and decreases to decrease refrigerant flow with decreases incompressor capacity.
 37. A control system of claim 33 wherein thepressure sensing mechanism measures pressure adjacent the input of theevaporator.
 38. In a vehicular air conditioning system including acompressor, a condenser, an evaporator and an accumulator connected inseries for cyclic refrigerant flow therein and wherein the vehicleengine drives the compressor so that the refrigerant pumping capacity ofthe compressor increases and decreases with increases and decreases invehicle speed, and the heat rejection capacity of the condenserincreases and decreases with air flow there through with increases anddecreases in vehicle speed and engine fan speed, a control systemcomprising: a pressure sensitive control valve having an input port, anoutput port, a valve between the input port and output port, and apressure sensing mechanism coupled to the valve for providing adisplacement movement thereto as a function of sensed pressure forcontrolling the size of the valve opening; means for coupling the inputand output ports of the pressure sensitive valve in the air conditioningsystem at a point adjacent the evaporator, and means for coupling thepressure sensing mechanism to sense refrigerant pressure adjacent theevaporator so that the valve functions as a variable orifice to controlthe amount of refrigerant flow trough the system for variations incompressor and condenser capacities in a direction to achieve heatabsorption over substantially the entire evaporator while interactingwith the accumulator by providing levels of liquid refrigerant flow asneeded to control the amount active charge of the refrigerant in thesystem.
 39. A variable orifice control system for vehicular airconditioning systems including a compressor, a condenser, an evaporatorand an accumulator connected in series for cyclic refrigerant flowtherein and wherein the vehicle engine drives the compressor so that therefrigerant pumping capacity of the compressor increases and decreaseswith increases and decreases in vehicle engine speed, and the heatrejection capacity of the condenser increases and decreases with airflow there through with increases and decreases in vehicle speed andengine fan speed, a control system comprising: a pressure sensitivecontrol valve having an input port, an output port a valve between theinput port and output port and a pressure sensing mechanism coupled tothe valve for providing a displacement movement thereto as a function ofsensed pressure for controlling the size of the valve opening; means forcoupling the input and output ports of the pressure sensitive valve inthe air conditioning system between the condenser and the evaporator,and means for coupling the pressure sensing mechanism to senserefrigerant pressure adjacent the evaporator so that the valve functionsas a variable orifice and interacts with the accumulator to vary theamount of refrigerant flowing in the system in a direction correspondingto changes in the compressor and condenser operating capacities.
 40. Avariable orifice control system as defined in claim 39 wherein thevariable orifice and accumulator interact of change the cooling capacityof the system in a direction to follow the compressor and condenseroperation capacities.
 41. A variable orifice control system as definedin claim 39 wherein the variable orifice interacts with the accumulatorto maintain the refrigerant charge of the system.
 42. In vehicular airconditioning systems including a compressor, a condenser, an evaporatorand an accumulator connected in series for cyclic refrigerant flowtherein and wherein the vehicle engine drives the compressor so that therefrigerant pumping capacity of the compressor increases and decreaseswith increases and decreases in vehicle engine speed, and the heatrejection capacity of the condenser increases and decreases with airflow there through with increases and decreases in vehicle speed andengine fan speed, a method for controlling the system comprising:sensing the pressure of the refrigerant adjacent the evaporator;controlling the flow of refrigerant through the evaporator with a valvethat is responsive to the sensed pressure so as to function as avariable orifice to control refrigerant in a direction to adjust thecooling capacity of the system as a direct function of the compressorand condenser capacities.
 43. The method as defined in claim 42 wherein:the controlling step adjusts the cooling capacity of the system toincrease as either or both the compressor and condenser capacitiesincrease.
 44. The method as defined in claim 43 wherein: the sensedpressure corresponds to the output pressure of the evaporator, and thecontrol step controls the flow of refrigerant in a direction so that thepressure at the output of the evaporator corresponds to saturated vaporwherein the refrigerant is substantially all vapor with a minor amountof liquid.
 45. The method as defined in claim 44 wherein: thecontrolling step interacts with the operation of the accumulator so asto provide levels of liquid refrigerant from the evaporator as needed tokeep the active refrigerant in the system charged.
 46. The method asdefined in claim 46 wherein: the sensing step includes adjusting thesensed pressure as a function of the flow rate of the refrigerant.